Strong polarization selectivity in 780-nm vertical-cavity surface-emitting lasers grown on misoriented substrates

We report that the 780 nm quantum well vertical-cavity surface-emitting lasers (VCSELs) grown on a 2° off misoriented (001) substrate toward (111)A exhibit a high polarization suppression ratio over a few hundred. The main polarization is always along the [-110] direction for all the lasers over the entire operating currents. To understand the physical origin of this polarization selectivity, the gain/loss difference between two competing polarization modes in VCSELs is investigated by measuring the subthreshold spectral linewidth. The obtained modal gain/loss difference is about 3.0 cm^-1, which is sufficiently large for polarization stabilization and amounts to 4% of the threshold modal gain. Comparison with the subthreshold measurement and previous theoretical work shows significant discrepancy, which implies the possibility of other polarization selection mechanisms inducing such large gain/loss differences in 780 nm quantum wells grown on a misoriented substrate. In addition, it is found that the 780 nm VCSEL made of a bulk active medium grown on a misoriented substrate also shows a high polarization selectivity as quantum well lasers.